Method and device for centerless cylindrical grinding

ABSTRACT

During centerless cylindrical grinding, attention must be paid to the fact that the workpiece ( 3 ) is placed in a very specific position between the grinding wheel ( 1 ), the regulating wheel ( 2 ) and the support guide ( 4 ). The optimal position of the workpiece ( 3 ) initially set cannot be maintained as a result of the progression of the grinding process and the changes caused by said process in the diameter and contour of the workpiece ( 3 ). The invention provides a solution to said problem, whereby height adjustment and/or the oblique position of the support guide ( 4 ) are automatically modified in accordance with the progression of the grinding process and during said grinding process with the purpose of achieving operationally optimal readjustment. The progression of the grinding process can be detected using measuring techniques, e.g. by measuring the diameter of the workpiece ( 3 ) or its deviation from roundness and using said measurement as output variable for adjusting the support guide ( 4 ).

[0001] The invention relates to a method for centerless cylindricalgrinding, for which the rotationally symmetrical workpiece is locatedbetween the grinding disk, the regulating wheel and the support guideduring the grinding process and for which the distance between thegrinding disk and the regulating wheel as well as the height setting ofthe support guide can be adjusted selectively during the grindingprocess.

[0002] A method of this type, which is frequently also referred to inpractice as “centerless method”, is known, for example, from the DE 3202 341 A1. In this publication, it is stated that the position of theworkpiece between the grinding disk, the regulating wheel and thesupport guide, optimum for the grinding process and required for anoptimum grinding result, cannot be adjusted easily. Since the regulatingwheel must also bring about the advance of the workpiece, it assumes aposition that is tilted slightly out of the horizontal. The workpiecelies in a manner, which cannot be defined precisely, between theregulating wheel and the support guide; in this position, it is pressedin by the grinding disk. It is advantageous here for the support guideto be also tilted slightly out of the horizontal. The determiningprocess parameters for preparing the machine for the grinding processare the axial distance between the grinding disk and the regulatingwheel, as well as the height adjustment of the support guide. For eachdiameter of a workpiece, there is a most suitable axial distance fromthe grinding disk and the regulating wheel and, for this, the mostsuitable height adjustment of the support guide must be found onceagain. The matching of these process parameters requires muchexperience.

[0003] So that the cumbersome adjustment by hand, optionally by trialand error and by test runs, will not have to be carried out whenever themachine is changed over to a new type of workpiece, it has already beenproposed in DE 32 02 341 A1 a particular height adjustment of thesupport guide be assigned to each axial distance between the grindingdisk and the regulating wheel. For this purpose, the regulating wheel ismounted in the usual manner in a headstock carriage, which can bescrewed down in the direction of the grinding disk. When the grindingdisk and the regulating wheel are adjusted to a particular axialdistance corresponding to a particular diameter of the workpiece, aforced mechanical coupling between the headstock carriage and thesupport guide causes a particular value for the height setting of thesupport guide to come about at the same time. According to the proposalof the DE 32 02 341 A1, said adjustment can also be made during thegrinding process when the contacting force of the grinding disk must becorrected. As a result, for each approach of the regulating wheel to thegrinding disk, the support guide is raised by a certain amount at thesame time.

[0004] However, the quite difficult processing position of theworkpiece, once set, changes very rapidly when the external diameter ofthe workpiece decreases during the grinding. This is the caseparticularly when the diameter changes greatly, as it does very rapidlywith the CBN grinding disks, the use of which is customary at thepresent time. However, if the optimum operating position of theworkpiece between the grinding disk and the regulating wheel isdisturbed, the grinding result also deteriorates; a labile position ofthe workpiece can also come about. In every case, the danger exists thatthe workpiece will be ground out of round. This deficiency cannot beeliminated with the known grinding device. Admittedly, by a selectiveadjustment by hand, the known grinding device permits some change in thedistance between the grinding disk and the regulating wheel in a forcedcoupling with the height adjustment of the support guide. However, thepossibilities of the device are no longer adequate to meet thepresent-day requirements for grinding accuracy in mass production.

[0005] It is therefore an object of the invention to provide a methodfor the centerless cylindrical grinding of the type named above, forwhich a position of the workpiece between the grinding disk, theregulating wheel and the support guide, required for an optimum grindingresult, is ensured even in material that has been abraded heavily duringthe whole of the grinding process.

[0006] This objective is accomplished in accordance with thecharacterizing part of claim 1 owing to the fact that the heightadjustment and/or the inclined position of the support guide are changedas required by the advancing grinding process and, during the latter,automatically in the sense of an operationally optimum adjustment.

[0007] The progress of the grinding process, which can be determined invarious ways familiar to those skilled in the art by measurement or byempirical values, accordingly is used as an influencing variable, inorder to adapt the position of the support guide to the contour of theworkpiece, which changes during the grinding process. The correctprocessing position of the workpiece during the grinding process thenleads to the greatest possible accuracy of the grinding result.

[0008] An advantageous development of the inventive method may consisttherein that, during the grinding process, the contour of the workpieceis determined by measurement and the support guide is adjusted dependingon the results of the measurement.

[0009] In so doing and in accordance with further advantageousdevelopments, the diameter of the workpiece can be measured continuouslyor at intervals. It is, however, also possible to measure deviations ofthe contour of the workpiece from the circular shape continuously duringthe grinding process and, when a certain value of the deviation isexceeded, to change the height setting and/or the inclined position ofthe support guide in the sense of eliminating this deviation. Thelast-mentioned possibility can be combined with the continuousmeasurement of the diameter of the workpiece. The use of theabove-mentioned influencing variables to adjust the support guide leadsto great accuracy and dimensional consistency of the ground workpieces.However, this method of working is very expensive.

[0010] In mass production, it will frequently be possible to work moreeconomically because the height adjustment and/or the inclined positionof the support guide are controlled by a fixed operating program, whichtakes into consideration the changes, required for a particular type ofworkpiece, takes place as a function of the grinding cycle and isrepeated for each individual workpiece. This development of the process,which is the object of a further advantageous development, accordinglyundertakes the grinding process of each individual workpiece of aconstant type in the form of an automatic program. If the number ofitems involved is sufficiently large, reliable typical values relatingto the optimum adjustment of the support guide during the grindingprocess can readily be obtained, so that such an automatic program alsoleads to very good results.

[0011] Depending on the shape of the workpiece, which is to be ground,it is also possible to proceed according to a further, advantageousdevelopment so that, during the grinding process, the end surface of theworkpiece is supported in the axial direction at its center of rotationby a fixed point, about which it is swiveled upward as a center ofrotation. This procedure comes into consideration, for example, forvalve bodies, which consist, as is known, of a valve head and a valvestem. The valve head and the valve stem can then be ground in a singleprocess.

[0012] If the ground workpiece must meet particularly exactingrequirements with regard to accuracy, the distance between the grindingdisk and the regulating wheel can also be altered automatically in thesense of an operational optimum adjustment in addition to the heightadjustment and/or the inclined position of the support guide. Since theregulating wheel and/or the grinding disk are generally mounted anyhowin an adjustable headstock carriage, this measure can be introduced inexisting grinding machines without excessive difficulties.

[0013] Finally, according to a last, advantageous development,provisions can also be made so that the central axle of the regulatingwheel is inclined with respect to the horizontal and in that the angleof inclination of the central axle is likewise adjusted automaticallyaccording to the demands of the advancing grinding process.

[0014] The invention also relates to a device for centerless,cylindrical grinding. In accordance with a device of DE 32 02 341 A1,named above, the starting point is a device for the centerless,cylindrical grinding with a driven grinding disk and a driven regulatingwheel, of which at least one is mounted in a headstock carriage, whichcan be adjusted transversely to the axial direction of the workpiece,and with a support guide, which supports the workpiece, is locatedbetween the grinding disk and the regulating wheel and the height ofwhich can be adjusted by means of at least one actuating drive.

[0015] To accomplish the objective already mentioned with regard to thedevice, especially for carrying out the method of one of the claims 1 to8, a control device is provided, which automatically actuates theactuating drive of the support guide during the grinding process in thesense of an adjustment optimum for the grinding process.

[0016] In contrast to the state of the art, the intervention by hand,which is difficult to estimate, is omitted thereby because, with thepossibilities known at the present time for accurately controlling thegrinding process, it is possible, on the basis of stored empiricalvalues or calculated values, to enter accurate process parameters forautomatically controlling the adjustment process.

[0017] From a mechanical point of view, the device can be configuredadvantageously so that two actuating drives are provided, which engagethe support guide, are connected with the control device and can beactuated by the latter independently of one another in such a mannerthat, during the grinding process, the inclination of the support guidewith respect to the horizontal can also be adjusted selectively.

[0018] Advantageously, adjusting spindles with CNC-controlled axes comeinto consideration as actuating drives, each adjusting spindle beingindividually controllable.

[0019] In particular, it is possible to proceed in such a manner, thattwo actuating drives, acting in the vertical direction in thelongitudinal direction of the support guide, engage the latter at adistance from one another.

[0020] For workpieces of a suitable shape, such as valve bodies, theinventive device can be configured particularly advantageously owing tothe fact that it has a support with a point, which is disposed in frontof the support guide in the longitudinal direction of the latter and isdirected towards the center of rotation of the workpiece, which is to beground. For a device so configured, an accurate axial fixing of theworkpiece during the grinding process is ensured so that, in spite ofdifferent external diameters and even when radial end surfaces orannular surfaces, which are to be ground, are present, an accurateresult comes about.

[0021] For many cases, it will suffice if the support guide is a single,continuous body. However, in the case of rotationally symmetrical bodieswith different diameter regions and according to a particularlyadvantageous proposal of the present invention, a supporting body,extending over the whole length of the support guide, is provided. Theactuating drives engage this supporting body, to which two or moresupport bodies are hinged, which are connected with the supporting bodyover swiveling axes extending transversely to the longitudinal directionof the supporting body and having different supporting heights. Thesupport guide thus consists of several parts. By means of the hingedsupport body, a workpiece with different allowances at the outerdiameters can be supported well at the support guide and therefore beground optimally.

[0022] If, at the same time, each support body is supported on eitherside of its swiveling axes by compression springs on the supportingbody, a self-adjusting zero position of the supporting body can beachieved in a simple manner.

[0023] This development can be optimized even further owing to the factthat the swiveling axis between a support body and the supporting bodyis mounted on the side of the support body and the supporting body in apre-tensioned bearing extending perpendicularly to the supporting body.The multi-part support guide becomes adaptable to such an extenttherewith, that even workpieces with stepped, different diameters can beground. By these means, it becomes possible to grind whole families ofparts on the same grinding machine without changing over the supportguide.

[0024] With regard to the control, the inventive device is configuredparticularly advantageously in accordance with a further proposal owingto the fact that a measuring device, by means of which the diameterand/or the deviations of the workpiece contour from the circular shapeare measured during the grinding process, is assigned to the supportguide and owing to the fact that the measuring device is connected withan evaluating unit, which, in turn, is connected for passing on controlsignals to the control unit.

[0025] A simpler and, for mass production, particularly well suiteddevelopment of the inventive device may, however, also consist thereinthat the control device is connected with a programming unit, whichsupplies control signals, required for grinding a particular type ofworkpiece, to the control unit according to a time-dependent operatingprogram and repeats for each individual workpiece of this type.

[0026] The invention is described below in even greater detail by meansof examples, which are shown in the Figures, of which

[0027]FIG. 1 basically illustrates the process of the centerlesscircular grinding, the machine column, the support guide as well as thegrinding disk and the regulating wheel, together with the workpiece,being shown only diagrammatically,

[0028]FIG. 2 contains a diagrammatic representation for adjusting thesupport guide by means of two actuating drives, corresponding to thesection A-A of FIG. 1,

[0029]FIG. 3 shows the grinding of a rotationally symmetrical workpiecewith different diameter regions and also corresponds to section A-A ofFIG. 1,

[0030]FIG. 4 is a view corresponding to arrow B of FIG. 3 and

[0031]FIG. 5 illustrates the principle of a multipart support guidecorresponding to section A-A of FIG. 1.

[0032] In FIG. 1, the process of centerless circular grinding is showndiagrammatically. A grinding disk 1 and a regulating wheel 2 aredisposed essentially with parallel axes next to one another. Theworkpiece 3 is on a support guide 4, which is provided with awear-resistant covering 5. The height of the support guide 4 isadjustable with respect to the machine column 10, as indicated by thedouble arrow 6. The central axes and, with that, also the axes ofrotation of the workpiece 3, of the grinding disk 1 and of theregulating wheel 2 are indicated by 7, 8 and 9.

[0033] So that the workpiece 3 can be caused to rotate, the regulatingwheel 2 must be driven rotationally that is, it must be rotated aboutits central axis 9. Through contact with the workpiece 3 at its outerdiameter, the latter is caused to rotate. For grinding the surface ofthe workpiece, the grinding disk 1 is also caused to rotate about itscentral axes 8. The directions of rotation of the grinding disk 1 and ofthe regulating wheel 2 are indicated by the curved directional arrows 11and 12. In the case of conventional and known machines for centerlesscircular grinding, the grinding disk 1 is taken up in a main headstockand the regulating wheel 2 in a regulating wheel headstock. One or bothheadstocks may be mounted movably in the x direction on a common machinecolumn 10. As is well known, the x direction is the one extendingtransversely to the longitudinal direction of the workpiece. Theconstruction of such headstocks and the driving mechanisms of the disksare customary in the art, so that the details are not shown.

[0034] The position of the workpiece 3 on the support guide 4 is notdefined as clearly as one might have expected from the diagrammaticrepresentation of FIG. 1. Namely, in order to achieve an advance, theregulating wheel 2 must be disposed with an axis tilted slightly fromthe horizontal. With that, the workpiece is also adjusted so as to beinclined somewhat downward, which can be compensated for by an inclinedposition of the support guide. So that the true-to-size surfaces, groundto a precise contour, come about, the workpiece must occupy a veryparticular position between the grinding disk 1, the regulating wheel 2and the support guide 4. However, a position, set ever so accurately atthe beginning of the grinding process, is changed rapidly once again ifthe diameter and the contour of the workpiece are changed as aconsequence of the grinding process. This is particularly the case withthe CBN grinding disks, which are customary at the present time.

[0035] The remedy consists therein that, during the grinding process,the support guide is raised further and also its inclination iscorrected, until the optimum relationships are restored and theworkpiece is ground cylindrically.

[0036] By means of a sectional representation of FIG. 1, FIG. 2therefore explains how the adjustment of the support guide takes placeduring the grinding process. For this purpose, the support guide 4 withthe workpiece 3 rests on two actuating drives 15 and 16, which, in turn,are supported on the machine column 10. The actuating drives are at adistance from one another in the longitudinal direction of the supportguide 4. In the example shown, the actuating drives are formed byadjusting spindles with CNC-controlled axes, each adjusting spindlebeing individually controllable. Parallel shifting of the control guideupward can be achieved owing to the fact that the two adjusting spindlesare controlled synchronously. If, in addition, it is necessary toincline the support guide 4 by the angle α with respect to thehorizontal, the actuating drive 16 must be shifted more than theactuating drive 15. The adjusting directions of the actuating drives aremarked in FIG. 2 by double arrows 13 and 14.

[0037]FIG. 3 also contains a representation corresponding to section A-Aof FIG. 1. The workpiece here is a valve body 17, which consists, in theusual manner, of a stem 18 with the valve head 19. Admittedly, herealso, the valve body 17 rests on a support guide 4. However, anadditional support 21 is fastened here by means of screws 22 to themachine column 10 and a point 20 is formed at the support 21. The frontsurface of the valve head 19 of the valve body 17 is supported at thispoint 20. Accordingly, it cannot happen that the valve body 17, underthe influence of the axial grinding forces resulting from grinding thebevel at the valve seat, can migrate in the axial direction out of thegrinding zone.

[0038] The central axis of the point 20 essentially is at the sameheight as the central axis of the grinding disk. The axis of rotation ofthe valve body 17 corresponds approximately to the central axis 23 ofthe point 20, as long as the support body is horizontal.

[0039] These relationships are shown even better in FIG. 4, whichcontains a view corresponding to arrow B in FIG. 3.

[0040]FIG. 5 illustrates a support guide 24 in a multi-partconstruction. It consists, to begin with, of a supporting body 25, whichis supported, in the same manner as to the support guide shown in FIG. 2by two actuating drives 15 and 16 at the machine column 10. An inclinedposition of the supporting body 25 can be achieved here also byadjusting the actuating drives 15 and 16 differently. What is differenthere, however, is that the supporting bodies 25 are hinged on twosupport bodies 26, 27. For this purpose, swiveling axes 28, 29, whichextend transversely to the longitudinal axis of the supporting body, areprovided. The support bodies 26, 27 are thereby connected in the form ofrockers with the supporting body 25. Their swiveling ability isindicated by the round arrows 35 and 36. The support bodies may havedifferent support heights.

[0041] On either side of the swiveling axes, the support bodies 26, 27are supported by compression springs 30, 31 and 32, 33 on the supportingbody 25. By these means, a zero position is reached easily for apossible oscillating movement of the supporting body 25, 26.

[0042] In the case of this construction, the support bodies 26, 27 canadapt themselves up to a certain degree to the workpiece, the diameterof which deviates from the nominal dimension. During the grindingprocess, the oscillating movement is compensated for by the processforces, which act on the support body and are superimposed on the springforces.

[0043] A further advantage of the multi-part support guide of FIG. 5consists therein that, due to the oscillating movement of the supportbodies 26, 27, workpieces of different diameters can be ground on thisguide. As a result, it is possible to grind complete families of partson the same machine without changing over the support guide. Largerdifferences in the diameter can also be equalized owing to the fact thatthe swiveling axis 28, 29, which is between a support body 26, 27 andthe supporting body 25, can be brought to different height positions byadjusting the two actuating drives 15, 16.

1.-17. (Cancelled)
 18. Method for centerless cylindrical grinding of arotationally symmetrical workpiece by means of a grinding machinecomprising a grinding wheel, a regulating wheel and a support guide, themethod comprising positioning the workpiece between the grinding wheel,the regulating wheel and the support guide, rotationally driving thegrinding wheel and the regulating wheel thereby to grind the workpieceand automatically adjusting elevation and inclination of the supportguide as a function of grinding progress.
 19. Method according to claim18, wherein the inclination of the support guide is adjusted byadjusting the height of the support guide independently at two sites onthe support guide spaced from each other in a direction parallel to theaxis of the workpiece.
 20. Method according to claim 19, wherein thegrinding machine further comprises a fixed structure having a point andthe workpiece has an end face in contract with the point whereby theworkpiece pivots about said point as the support guide is adjusted. 21.Method according to any one of claims 18 to 20, further comprisingautomatically adjusting axial inclination of the regulating wheel as afunction of progress of the grinding.
 22. Apparatus for centerlesscylindrical grinding, comprising a grinding wheel, means forrotationally driving the grinding wheel, a regulating wheel, means forrotationally driving the regulating wheel, a headstock carriage on whichat least one of the grinding wheel and the regulating wheel is mounted,a support guide located between the grinding wheel and the regulatingwheel for supporting a rotationally symmetrical workpiece for rotationabout an axis of rotational symmetry of the workpiece, the headstockcarriage being adjustable transversely to said axis, at least oneactuating drive for adjusting height and inclination of the supportguide, a control for automatically actuating the actuating drive duringgrinding of the workpiece thereby to adjust height and inclination ofthe support guide, and a source of programmed control signals for thecontrol so that the adjustment of the height and inclination of thesupport guide is correlated with progress of the grinding.
 23. Apparatusaccording to claim 22, wherein the at least one actuating drivecomprises first and second independently actuatable actuating drives.24. Apparatus according to claim 23, wherein the first and the secondactuating drive is each connected to the support guide at a respectiveone of said two sites.
 25. Apparatus according to claim 24, wherein theactuating drives comprise adjusting spindles and the control comprises aCNC, axes of the spindles being controlled by the CNC.
 26. Apparatusaccording to claim 25, further comprising means defining a fixed pointfor engaging an end face of the workpiece at a point on said axis, saidfixed point being spaced from the support guide away from the grindingwheel and the regulating wheel in a direction parallel to said axis. 27.Apparatus according to claim 26, wherein the support guide comprises afirst body to which said actuating drives are connected and second andthird bodies mounted on said first body for supporting the workpiece attwo different elevations at respective two locations spaced from eachother in a direction parallel to said axis and respective means forsupporting the second and third bodies for rocking of each about arespective axis transverse to said workpiece axis.
 28. Apparatusaccording to claim 27, further comprising for each of the second and thethird bodies a respective pairs of compression springs, each compressionspring having one end engaging the second or the third body and anotherend engaging the first body, the springs of each said pair being spacedon opposite sides of the transverse rocking axis of the respectivesecond and third bodies in directions parallel to the axis of theworkpiece.